In the related art, as blood pumps which transport blood, there have been known turbo-type pumps which send out blood in response to centrifugal force. The turbo-type pump includes a hollow housing, an impeller that is rotatably accommodated inside the housing, a rotary axis (i.e., shaft member) that serves as a rotation center of the impeller, an upper portion bearing that rotatably supports an upper end portion of the rotary axis, and a lower portion bearing that rotatably supports a lower end portion of the rotary axis (see, e.g., Japanese patent 4548450).
In the blood pump disclosed in Japanese patent 4548450, the housing is provided with an inlet port through which blood flows in, and an outlet port through which blood flows out. The inlet port and the outlet port are tubularly formed so as to protrude from the housing. In addition, the inlet port is provided so as to be an extension of the shaft member such that a central axis thereof coincides with the rotational axis of the rotary shaft member.
Recently, blood pumps in which the inlet port is provided so as to include an inclined section with respect to the rotary axis have been adopted. The outer profile of the inclined inlet port intersects an intermediate portion of the shaft member, and the pump housing typically includes a recessed portion or pocket that is coaxially aligned with the shaft member at the middle of the inlet port and receives an upper bearing installed inside the recessed portion for the shaft member.
However, in such a configuration, a circulation flow (reverse flow) of blood in the same direction as the rotational direction thereof is generated as a result of viscous drag at the outer periphery of the shaft member. When the circulation flow runs into (meets) a flow of blood flowing down through the inlet port, a retained portion (i.e., stagnant portion) of the blood is generated inside the inlet port. As a result thereof, in a case where the blood pump is used for a long time, there is a possibility that a thrombus may be formed inside the recessed portion, particularly at an outer peripheral portion of the shaft member or upper bearing.